168 CONVERGENCE IN MINUTE STRUCTURE 



comparison. The phenomena of intracellular 

 digestion, phagocytosis, and wandering cells come 

 under this category. An elaborate case is that 

 of the pulsating, multinucleated chromatophores 

 of eight-armed Cephalopoda. In Octopus, under 

 certain conditions of excitement, the play of 

 colour may be observed taking place with 

 marvellous regularity and rapidity. Each chrom- 

 atophore, as Chun l has demonstrated, is a single 

 disc-shaped cell with contractile processes radi- 

 ating from the periphery ; and these contractile 

 processes originate from the cell-body in the 

 same manner as the pseudopodia of a rhizopod 

 Protozoan. 



The preceding examples bear witness to the 

 truth of the conclusion that convergence depends 

 equally upon the unity of plan of composition 

 of the body of animals, as indicated in the 

 incidence of planes of symmetry, and upon the 

 continuity of the system of functions from 

 Protozoa to Metazoa. 



Now, if we stop for a moment to enquire what 

 is the bearing of all this, it may be said that I 

 have failed in my purpose unless it has been 

 made abundantly clear that the influence of 

 convergence in evolution has been widespread, 



1 Carl Chun, " Ober dieNatur und die Entwicklung der Chrom- 

 atophoren bei den Cephalopoden." Verh. d. Deutschen Zool. Ges., 

 1902, pp. 162-182. 



